Trump: 'Very disappointed' Mitt Romney declined debate

"I was disappointed that Mitt Romney, who's been up to see me at Trump Tower and called me and, you know, we've had numerous calls, wants very much to have my endorsement, I was actually very disappointed that he didn't do the debate, I was actually surprised," said Trump on CNN's "Piers Morgan Tonight" Wednesday.

Trump told CNN that the former Massachusetts governor called him personally to say he could not participate in the debate.

"He couldn't have been nicer. I mean, he said, 'Donald, I'm so busy and that day I had roped off for something else.' You know, he could not have been nicer, but still I was surprised," Trump said.

Political pundits and some GOP presidential candidates have been highly critical of the choice to have Trump moderate an upcoming Republican debate hosted by the conservative media outlet Newsmax.

Rep. Ron Paul (Texas) and former Utah Gov. Jon Huntsman declined to participate and publicly blasted the forum.

Huntsman has been very vocal about his opposition in media appearances, slamming the debate as a "joke." "I believe that the presidency of the United States of America is beyond reality shows," said Huntsman on NBC's "Today" show Tuesday.

Earlier this week, Trump dismissed Paul and Huntsman, calling them “joke candidates,” and said he doesn't believe either has a chance of winning the Republican nomination.

When asked to respond to Huntsman's comments on "Piers Morgan Tonight," Trump scaled back his negative rhetoric and called Huntsman a "nice guy."

"I'll be honest, I don't know him at all, but he actually looks like a nice guy and he seems like a nice guy," Trump said.